Japanese Patent Application Laid-Open No. 2002-222410 discloses an image diagnosing apparatus that measures body adipose of a subject based on a tomographic image of the subject acquired from a medical tomographic apparatus. The image diagnosing apparatus sets a boundary between subcutaneous adipose and visceral adipose with respect to a peripheral edge of a muscle region by a rolling ball method. This has a problem that the subcutaneous adipose and the visceral adipose are sometimes improperly separated depending on individual differences among subjects. The image diagnosing apparatus also has a problem of an unclear image display of a measurement result. Further, the image diagnosing apparatus extracts, as an adipose region, a region where a CT value is within a threshold range set by an operator. This causes an unnecessary minute adipose region such as feces remaining in intestine to be included in the extraction region, and for precise measurement, the operator has to manually remove the unnecessary region. The image diagnosing apparatus sequentially performs the steps of extraction of a body surface region of interest, extraction of a total body adipose region, extraction of a visceral region of interest, extraction of a visceral adipose region, and calculation of body adipose. This has a problem that each step includes many computations, and enhancing the speed of the processing is not considered.